Pittsburgh has flights to Seattle. https://www.usatoday.com/story/travel/flights/todayinthesky/...
Also, Northern Virginia is the location of Dulles. Montgomery county would also use Dulles or BWI which has 3 flights per day. Interestingly, with traffic, Washington D.C. is not within 45 minutes of Dulles so Washington D.C. is probably just looking at Reagan which has 1 flight per day to Seattle.